Nested RAID and booting

For financial reasons, I have had to temporarily create two members
of a RAID6 array by first creating a pair of RAID0 arrays from four member
disks. The RAID6 array is currently re-shaping, and so far all seems well.
I do have a concern about what will happen when the system reboots, however.
In order to properly assemble the RAID6 array, the two RAID0 arrays will
first need to be assembled and running, correct? How do I guarantee the two
RAID0 arrays will be up before mdadm attempts to assemble the RAID6 array?
Will simply putting them in the mdadm.conf file prior to the RAID6 array do
the trick?

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Re: Nested RAID and booting

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On Wed, 8 Jun 2011 00:54:44 -0500
"Leslie Rhorer" wrote:

> Will simply putting them in the mdadm.conf file prior to the RAID6 array =
do
> the trick?

Seems to work just fine for me.

Well, I also have the member array explicitly listed in a DEVICE clause,
together with physical drives. So I am not really sure if the default
"DEVICE partitions" would also include MD devices.

So in my mdadm.conf I have, roughly:=20

DEVICE /dev/disk/by-id/ata-WDC_WD20EADS-*-part*
DEVICE /dev/disk/by-id/ata-WDC_WD15EADS-*-part*
DEVICE /dev/disk/by-id/ata-Hitachi_HDS*-part*
DEVICE /dev/md1
ARRAY /dev/md1 UUID=3D...................................
ARRAY /dev/md0 UUID=3D...................................

....where md1 is a member of md0.

--=20
With respect,
Roman

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Re: Nested RAID and booting

These days most ( all? ) distributions use udev for plug and play. When
the physical disks are detected, udev notices ( with blkid ) that they
are raid members, and runs mdadm --incremental on them. Once they are
all detected, the array goes active, and udev runs blkid on the array,
notices that is a component, and runs mdadm --incremental on that.

On 6/8/2011 1:54 AM, Leslie Rhorer wrote:
>
> For financial reasons, I have had to temporarily create two members
> of a RAID6 array by first creating a pair of RAID0 arrays from four member
> disks. The RAID6 array is currently re-shaping, and so far all seems well.
> I do have a concern about what will happen when the system reboots, however.
> In order to properly assemble the RAID6 array, the two RAID0 arrays will
> first need to be assembled and running, correct? How do I guarantee the two
> RAID0 arrays will be up before mdadm attempts to assemble the RAID6 array?
> Will simply putting them in the mdadm.conf file prior to the RAID6 array do
> the trick?

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